Surgical sterilization method

ABSTRACT

A method and apparatus for sterilizing articles such as surgical and dental instruments by immersing the articles in a container of boiling tetrachloroethylene. The container has a lower, heated portion, a cooled upper portion wherein vapor from the boiling liquid condenses, and an intermediate vapor column. Articles to be sterilized are cleaned and then submerged in the boiling liquid for up to about 16 minutes; then the articles are raised slowly through the vapor to thereby exit the container, sterile and dry. The container may be provided with a sliding lid, with thermostatically controlled high temperature cut-offs for the heating element disposed in the lower portion, and in the upper portion of the container.

United States Patent [191 Tabone [451 Dec. 18, 1973 1 1 SURGICAL STERILIZATION METHOD [76] Inventor: Donald J. Tabone, 638 Benner Rd.

N 0. 202, Allentown, Pa. 18104 [51] Int. Cl. A611 l/00, A611 3/00 [58] Field of Search 424/351; 21/58, 2, 21/99, 83, 8587, 89, 90, 92, 93; 134/10, 12,

[56] References Cited UNITED STATES PATENTS 1,187,498 6/1916 Castle 21/92 1,827,479 10/1931 Lierman 21/87 1,850,524 3/1932 Whittaker... 21/87 2,096,737 10/1937 Dinley 134/40 X 2,207,186 7/1940 Wolff 134/10 X 2,231,790 2/1941 Andress 21/87 2,294,087 8/1942 Johnson 21/89 2,786,245 3/1957 Steinbeck 21/105 3,419,346 12/1968 Nicholas 21/87 3,459,490 8/1969 Fiihring et a1. 21/2 X 3,579,290 5/1971 Pickstone 21/2 FOREIGN PATENTS OR APPLICATIONS 167,297 12/1950 Austria 424/351 Primary ExaminerBarry S. Richman Attorney-Le Blanc & Shur [5 7 ABSTRACT A method and apparatus for sterilizing articles such as surgical and dental instruments by immersing the articles in a container of boiling tetrachloroethylene. The container has a lower, heated portion, a cooled upper portion wherein vapor from the boiling liquid condenses, and an intermediate vapor column. Articles to be sterilized are cleaned and then submerged'inthe boiling liquid for up to about 16 minutes; then the articles are raised slowly through the vapor to thereby exit the container, sterile and dry. The container may be provided with a sliding lid, with thermostatically controlled high temperature cut-offs for the heating element disposed in the lower portion, and in the upper portion of the container.

3 Claims, 5 Drawing Figures PAIENIED DEC 1 8 I975 SHEET 2 BF 2 FIGS SURGICAL STERILIZATION METHOD This invention relates to a sterilization method and apparatus particularly adapted for use with medical apparatus and surgical and dental instruments. The invention includes the discovery that boiling tetrachloroethylene (C Cl is an excellent sterilant. As will be subsequently explained, although this invention is not limited thereto, it is particularly adapted for continuous operation in medical and dental facilities to rapidly and efficiently sterilize instruments when desired without utilization of expensive and cumbersome equipment, or time consuming procedures.

Tetrachloroethylene, more generally known by its industrial name, perchloroethylene, is a relatively nonvolatile liquid having a boiling point of 250.5 degrees Fahrenheit. The liquid has no flash point, and has a specific gravity of 1.623. The colorless vapor, however, is 5.72 times heavier than air. lts residue upon evaporation is 0.001 percent by weight (non-volatile.)

This compound is a well known solvent and has been utilized for many years as a cleaning fluid for textiles and in vapor degreasing processes for metals. There is, however, no prior application of tetrachloroethylene known in the field of sterilization.

The purpose of sterilization is to destroy all pathogenic organisms and their spores which may be in or on the material being sterilized. It is never sufficient to destroy most or nearly all microorganisms present because their rate of reproduction is so great that in a short period of time the few which remain will multiply to the point of contamination.

Bacteria in their vegetative form are destroyed comparatively easily by a variety of methods. Spores, however, formed by a number of surgically critical organisms such as those of tetanus, anthrax, and gasgangrene are far more resistant.

Sterilization, in the past, has generally been achieved through the use of time consuming procedures, cumbersome equipment, or dangerous chemicals. There are three major methods in use, each of which has been found to be undersirable under certain circumstances. These methods use steam, dry heat, or chemicals such as ethylene oxide.

Traditionally steam sterilization in an autoclave has been the method most frequently employed. Saturated steam under pressure is dependable and easily controlled, and is currently used in hospitals and large institutions for sterilizing the bulk of surgical instruments and materials.

A pressure sterilizer or autoclave is essentially a chamber which is surrounded by a steam jacket. Steam is admitted to the jacket until the pressure reaches approximately 15 18 psi. The jacket steam is then allowed to flow into the chamber. The saturated steam enters at the top and rear of the unit, and forces the air withinthe chamber down and out through the chamber screen anddrain line. The air passes through the drain line and a thermostatic valve to a vertical pipe which acts as a vent to the atmosphere at the top, and a drain at the bottom. The thermostatic valve remains open until steam following the air heats the valve. The elements of the valve then expand and close.

After a period of time sufficient to sterilize the object has elapsed, the chamber is vented and cooled, and the sterile articles are dried. The heating and venting and drying phases in pressure sterilization are responsible for long total time cycles. The heating and venting phases may be shortened through use of a high vacuum to draw the steam into the chamber and to evaporate the condensate within the chamber after sterilization is completed. However, a typical autoclave cycle requires saturated steam at 121C and 15 pounds pressure for 20 minutes or more, depending on the volume of material being heated, in order to assure sterility.

The primary disadvantage in the use of steam sterilization is the long time factor, but other problems due to mechnical breakdowns, and operator errors, are also presented frequently. Also, there are some items such as plastics, rubber, wool, leather, glycerin, petroleums, powders, as well as the cutting edges of certain instruments which can not be subjected to either the elevated temperatures of an autoclave or to the moisture and must be sterilized by other methods.

Dry heat procedures are normally utilized for materials such as anhydrous oils, petroleum products, instruments which can not be disassembled, sharp instruments which might be damaged by heat, and glassware. Because dry heat penetrates very slowly and unevenly, an extremely long exposure period is required. This procedure is also unsuitable for sterilization of heat sensitive fabrics and rubber goods.

The equipment normally utilized in dry heat sterilization is an electrically heated oven. The oven may optionally be equipped with a blower for forced air circulation.

As in the case of steam sterilization the principal disadvantage in hot air or dry heat sterilization involves a long time factor for exposure, which may be up to 6 hours or longer at 250 degress Fahrenheit. Also the need for perfectly clean instruments before sterilization, elaborate material charts for various materials and limitations on load size and density are important considerations.

The third and newest method of sterilization involves the use of ethylene oxide gas as described for example in US. Pats. No. 2,891,838 and 3,238,096. Ethylene oxide has the advantage of effectiveness at relatively low temperatures, and good penetration ability. Also this sterilant does not corrode or otherwise damage metal, paper, plastics, rubber, leather, wood, or wool.

Similar to the aforementioned methods the principal disadvantage associated with ethylene oxide is a long time factor for exposure and aeration, normally between 12-30 hours, necessary to eliminate the highly toxic residue from the treated articles. There is an ever present, although small, danger of tire. Finally, because of the extremely long time cycle, it is necessary, when sterilizing with ethylene oxide, to have many duplicate sets of instruments available for use while others are being sterilized.

By utilizing the sterilization method and apparatus of this invention, the major disadvantages associated with prior methods may be overcome. it has been discovered that sterilization with boiling tetrachloroethylene may be achieved much more rapidly, e.g., in about 16 minutes.

In addition, the apparatus of this invention permits continuous operation by maintaining the sterilant as a boiling liquid with the vapor therefrom continuously Condensing within the apparatus and returning to replenish the liquid sterilant. Another important advantage is that the articles emerge through the vapor column in a dry condition.

The apparatus of this invention comprises a container which is heated and thermostatically controlled to maintain the tetrachloroethylene liquid contained therein at its boiling point. The apparatus also provides a vapor column above the boiling liquid containing tetrachloroethylene vapor at or near the boiling temperature. Spaced above the vapor column is a cooled freeboard area for condensation of the vapor. Preferably a water jacket surrounds the freeboard area with circulating water to act as a coolant. As the vapor rises into the cooled freeboard area the vapor condenses and returns to the boiling liquid below. In the alternative a refrigeration unit with a circulating coolant such as Freon may be substituted for the water jacket.

Because the vapor is heavier than air it normally does not escape from the container. The articles to be sterilized are placed in an open mesh basket and lowered into the boiling liquid. At the expiration of between 12 and 16 minutes, the container is opened and the basket slowly raised through the vapor. The sterilized articles are normally at the vapor temperature when taken from the container. Accordingly, they emerge from the container dry. The basket should be raised slowly to avoid pulling vapor from the container.

The apparatus and method according to this invention have several important advantages. For example, the apparatus can be made small and convenient to install, requiring only a source of electricity and running water if a water jacket is used. Thus, the apparatus is particularly adaptable for use in a doctors or dentist's office where only small numbers of instruments must be sterilized, but where speed and convenience are of great importance.

Likewise, because the sterilant employed is quite safe and easy to handle sterilization according to this invention requires few safety precautions, and the apparatus may be located directly in the examining room.

Also, the invention is adaptable with equal facility to large as well as small scale operations and to utilization with medical apparatus as well as surgical and dental instruments.

Accordingly, it is an object of this invention to provide a rapid, effective, and inexpensive method and apparatus for sterilization.

It is another object to provide an apparatus adapted to maintain tetrachloroethylene at its boiling point, with condensation of the vapor formed for reuse as a boiling liquid in the sterilizing procedure.

It is another object to provide a method and apparatus for sterilizing nonporous articles such as surgical and dental instruments which method will not damage or corrode the cutting edges of these instruments.

It is still another object to provide a method and apparatus for sterilizing instruments and medical apparatus wherein, due to rapid sterilization procedures, duplicate banks of instruments are not needed.

A further object of this invention is to provide a sterilization technique particularly adaptable for safe and convenient use in a doctor's or dentists office and also for large scale use in hospitals or other institutions.

It is yet another object to provide a sterilization machine comprising a container with a heated lower portion and a condensing cooled freeboard area spaced thereover, the chamber and the freeboard area connected by a vapor column whereby articles to be sterilized may be maintained in the boil chamber until sterilization is completed, and then raised slowly through the vapor area to emerge from the apparatus dry and sterile.

These and other objects will become readily apparent with reference to the following drawings and description wherein:

FIG. 1 is a perspective view of the apparatus of this invention with portions broken away for clarity of illustration.

FIG. 2 is a top plan view of the device of FIG. 1 with the cover removed.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2 showing the basket in a lowered position.

FIG. 4 is a cross-sectional view taken along line 44 of FIG. 3 showing the basket in a raised position.

FIG. 5 is a cross-sectional view taken along line S5 of FIG. 3.

With attention to FIGS. 1 and 3, the sterilization device of this invention includes a housing 12 having a slidable top 14 with a handle 15 mounted thereon. In a preferred embodiment, top 14 is mounted by a depending guide 16 which engages track 18 on housing 12. This invention is not intended to be limited by the shape of the device shown in FIG. 1 or by the method of mounting the top 14, and comprehends any conventional shape or mounting. A sliding door, however, is preferred to minimize any suction effect on the gaseous contents of the device 10 when the top 14 is opened.

An insulated container 20 is mounted within the lower and central portions of housing 12, and the upper portion thereof mounts a hollow jacket 22 for circulating coolant.

A vertical panel 24 on housing 12 mounts controls as will be subsequently described. A coolant inlet 26 and an outlet 28 coupled to jacket 22 by conduits 27 and 29, respectively, extend through control panel 24. A drain outlet 30 from container 20 extends through housing 12. Knob 32 on panel 24 controls the flow through the drain outlet 30.

In the preferred embodiment, additional controls include a thermometer 33 and two thermostats 34 and 36 shown in FIGS. 2, 3 and 5, disposed, respectively, within housing 12 attached to the lower surface of container 20 and in the upper portion adjacent jacket 22. The thermometer registers the temperature of the sterilant within container 20, and the thermostats function as safety devices to regulate the internal temperature of device 10.

Referring to control panel 24, FIG. 1, thermostat 34 functions as a high temperature cut-off control. If the temperature in container 20 exceeds a preselected maximum, as for example, if the sterilant inadvertently drains from the container, thermostat 34 coupled to switch 38 by electrical leads shown in FIG. 5, actuates switch 38 which functions as a circuit breaker to uncouple the electrical heating unit 40, shown in FIG. 4, from its power source (not shown) and to light warning light 42. The heating unit 40 may be re-energized by depressing switch 38. Knob 44 on plate 46 functions to calibrate thermostat 34.

Thermostat 36 functions as a vapor level indicator. In the event the temperature adjacent jacket 22 exceeds a preselected maximum, as for example, if conduits 27 or 29 become clogged, thermostat 36 coupled to switch 48 by electrical lead 37 shown in FIG. 3, actuates switch 48 which also functions as a circuit breaker to uncouple the electrical heating unit 40 from its power source and to light warning light 42. The heating unit 40 may be re-energized by depressing switch 48. Knob 50 on plate 52 functions to calibrate thermostat 36.

Optional control features which are also preferred are a conventional timer 54, an on-off switch 56 for device 10, and a pilot light 58 to indicate when the switch 56 is in the on position and device is in operation.

The control elements described above are all well known commercially available components. The controls described herein are preferred components, only, and the substitution of other well known equivalent controls is comtemplated within the scope of this in vention.

With attention to FIGS. 3 and 4, the insulated chamber has a sloping bottom 60. Bottom 60 slopes to a central drain 62. Drain 62 is controlled by valve 64 which in turn is operated by rotation of knob 32 and shaft 66. When valve 64 is opened, liquid within chamber 20 drains by gravity through conduit 68 and outlet 30.

Liquid sterilant within chamber 20 is heated, in the preferred embodiment, by resistor type electrical strip heaters 40 attached to the underside of bottom 60. Heaters 40, as described above, are coupled to emergency switches 38 and 48, and to on-off switch 56, and are adapted to be coupled to a power source (not shown) by electrical leads 70 in FIGS. 1, 2, and 3 by any conventional method. As shown in FIG. 5 thermostat 34 is also attached to the underside of bottom 60.

Articles to be sterilized are place in open mesh basket 72 and lowered by handles 73 or 74 into chamber 20 until feet 75 rest on bottom 60. An open mesh basket is preferred to minimize a piston effect on the liquid and vapor within the container 20 when the basket is lowered. It will be obvious that any type of handle for basket 72 may be utilized within the scope of this invention. Handles 73 and 74 are merely preferred types.

The level of liquid sterilant should be maintained, as shown by dashed line 76 in FIGS. 3 and 4, at about midway between the bottom 60 of the container 20 and the jacket 22. The height of basket 72 should be sufficient to permit total submersion in the sterilant as shown in FIG. 3. Handle 73 permits raising and lowering of basket 72 without reachinginto the heated vapor space below jacket 22. Handles 74 may also be utilized to suspend basket 72 in container 26 above the sterilant and below jacket 22 as shown in FIG. 4.

With attention to FIG. 5, coolant for jacket 22, perferably water directly from the mains, is admitted through conduit 27, the passage therethrough being controlled by a valve 68. Valve 68 may preferably be a preset automatic diaphragm valve adapted to open and close responsive to the temperature of the water passing therethrough.

Referring to FIG. 4, the freeboard height (f) in relation to the width (w) is found to be an important factor in achieving proper operation. In particular, to prevent vapor escape, it is found that the freeboard (f) should equal or exceed one-half the width (w).

To operate the device 10 of this invention, the drain valve 64 is closed by rotation of knob 32 and tetracholoroethylene is added to the chamber 20 up to about line 76. Cover 14 is then closed and the heating elements 40 actuated by switch 56. A coolant such as water is also admitted through conduit 27 and valve 78 to jacket 22 to be returned via conduit 29 to a drain (not shown).

When the liquid tetracholorethylene reaches the boiling point vapor will rise from the surface thereof and occupy the area within the chamber 20 above the liquid to the exclusion of air. As the vapor reaches the jacket 22 it will condense and return to the boiling liquid to thereby permit continuous operation without the addition of liquid sterilant.

The articles to be sterilized are then placed in basket 72, cover 14 is retracted, and basket 72 is lowered into chamber 20 until feet rest on bottom 60. Cover 14 is then displaced to close the housing 12. When thermometer 33 registers the boiling point of the sterilant, i.e. 250F. then timer 54 is set for up to about sixteen minutes.

At the timer signal, cover 14 is retracted and the basket slowly raised from the liquid. In order to dry the instruments, it has been found that if the basket remains in the vapor for a short while, the instruments may be removed from the device in dry condition, ready for use.

In an embodiment of this invention anticipated for use with medical or dental instruments, in a doctors examining room, chamber 20 has inside dimensions of ten and one half inches by six and one half inches by seven and three fourth inches high. The height of line 76 from bottom 60 is about 4 inches. The vertical thickness of jacket 22 is three and one fourth inches. The external dimensions of housing 12 are 15 inches by 8 inches by thirteen and one half inches high. For a device of this size, if basket 22 is raised from the bottom 60 at a rate of about 1.4 to 2.0 inches per second, instruments therein will emerge from the device dry.

In order to establish the effectiveness of tetrachloro ethylene as sterilizing agent a wide variety of tests were conducted against a total of six pathogenic organisms.

The tests, as will be hereinafter described, dealt with the effectiveness of tetrachloroethylene against two types of organisms. In the first group well-known pathogenic microorganisms were subjected to boiling tetrachloroethylene for varying times to establish the sterilizing potential of this chemical against bacteria which are not notably resistant to sterilization techniques. The second group of tests involved evaluation of the sterilization potential of boiling tetrachloroethylene against highly resistant strains of pathogenic micro-organisms, generally referred to as endospores, or spore forming bacteria.

EXAMPLE 1 48 hours at 35 C. and then visually examined for mi crobiogrowth.

Upon evaluation, none of the cylinders exhibited any growth. Accordingly, it was concluded that the three microorganisms tested were all effectively killed after no more than a ten minute submersion in boiling tetrachloroethylene.

EXAMPLE 2 In order to evaluate the effectiveness of tetrachloroethylene against spore-forming bacteria, cultures of the following were tested.

Mycohaclerium tuberculosis Pseudomonas aeruginosa Clostridium perfringens Glass beads having a 3 millimeter diameter were coated with actively growing microorganisms freshly isolated from human specimens. The beads were then placed in a beaker of boiling tetrachloroethylene and the beaker immersed in boiling tetrachloroethylene contained in a steel vessel. The upper portion of the vessel was surrounded by circulating coolant, i.e., water, so that the vaporized tetrachloroethylene would condense and return to the boiling liquid. Timing began when the glass beads contacted the boiling tetrachloroethylene.

In addition, glass beads inoculated with Clostridium perfringens were placed in sterile test tubes containing boiling tetrachloroethylene, two beads per tube. The temperature of the tetrachloroethylene therein was maintained at 250 degrees Fahrenheit throughout the time period.

At periodic time intervals beads were removed and placed in appropriate culture media for observation of growth.

Lowenstein-Jansen medium was used for Mycobacterium tuberculosis, tyrpticase soy broth and fluid thioglycollate medium for Pseudomonas aeruginosa, and fluid thioglycollate medium for Clostridium perfringens. All studies were performed in duplicate and control cultures were maintained by using inoculated beads not exposed to tetrachloroethylene.

At 2 minute intervals up to 20 minutes, beads were extracted from the boiling solution, placed in growth medium, and incubated as in Example 1 above to determine whether growth could be observed. The following table summarizes the results of duplicate tests with these microorganisms.

As shown above M. tuberculosis and Ps. aeruginosa as well as the vegetative strains of Example I were killed with less than a minute exposure and probably with less than a 2 minute exposure to boiling tetrachloroethylene. However, exposure for about l2 or more than 12 but less than 16 minutes is required to kill the more resistant Cl. perfringens.

Based on the foregoing tests of representative pathogenie microorganisms, it was concluded that articles are sterilized according to this invention by exposure to boiling tetrachloroethylene for a period of up to about 16 minutes.

In summary, this invention comprises a method and apparatus for sterilization with boiling tetrachloroethylene to rapidly and effectively sterilize articles such as surgical and dental instruments. A major advantage in using tetrachloroethylene stems from the short time period needed to sterilize articles in the boiling liquid. In addition, by utilizing the apparatus of this invention it is unnecessary to maintain several duplicate sets of instruments because, following usage, contaminated instruments may be quickly sterilized without the utilization of large and cumbersome equipment.

The apparatus of this invention, in a preferred embodiment, may be maintained in continuous operation for extended periods of time. The sterilant vaporizes, rises within the apparatus to a point where it enters a cooled upper area, and condenses to be boiled as a liquid.

The device also includes a thermostatically operated vapor level control which functions to shut off the heating element if the coolant supply fails. This control minimizes complete vaporization of the sterilant and escape thereof from the device. A second thermostatically controlled safety device is mounted adjacent the heating element, beneath the chamber. This device is utilized to shut off the heating element if the temperature within the chamber rises above a preselected maximum, such as the boiling point of tetrachloroethylene. A rise in temperature within the chamber, above the boiling point, could be caused by loss of the liquid sterilant during operation.

Tetrachloroethylene is uniquely suited for use as a sterilant because, in addition to its newly discovered anti-microbial qualities, the liquid'is relatively inexpensive, and safe to handle. In addition, the liquid is uniquely suited for continuous operation in the device of this invention because the vapor from the boiling liquid, being heavier than air will remain at the liquid surface unless agitated or sucked from the container. Ac-

cordingly, it is unnecessary to seal the container to keep the vapor from escaping. The use of a sliding cover and an open mesh basket, as described hereinabove, minimizes the disbursement of vapor when the container is opened and when the articles to be sterilized are placed therein or removed therefrom.

This invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are Test A Test B 2 4 6 12 16 .20 2 4 6 12 16 20 t musm Control min. min. min. min. min. min. Control min. min. min. min. min. mm.

M. lubrrc'ulosis. Ps. aeruginnsa" Cl. pcrfrmgens.

NoTE: Growth; =No Growth.

therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

l. A method for sterilizing surgical and dental instruments comprising the steps of placing the instruments in an open mesh basket; submerging said instruments in said basket in boiling tetrachloroethylene for at least twelve minutes until all viable organisms thereon are no and about sixteen minutes.

Batu} December 18, 1974 Patent No,

Donald J.

Tabone Inventor(s) It is certified that error appears in the: above-identified patent Patent are 'i'zereb -y corrected shown below:

and that said Letters In Col. 5, line 29, "place" should read -,-placed.'

In Col. 77 after line 44,

and before the paragraph beginning "Ae shown above the table for ExanipleiII should be inserted.

Signed and sealed this 18th day June 1974;

c. MARSHALL DANN Commissioner of Patents (SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer 

2. The method of claim 1 wherein said boiling liquid occupies the bottom portion of a chamber and a portion of said chamber over said liquid is occupied by tetrachloroethylene vapor, said step of drying further comprising slowly raising said basket through said vapor to dry the instruments therein before said basket is removed from said chamber.
 3. The method of claim 2 wherein said instruments are submerged in said boiling liquid for between twelve and about sixteen minutes. 